BMI introduction
BMI is a measurement of a person's leanness or corpulence based on their height and weight, and is intended to quantify tissue mass. It is widely used as a general indicator of whether a person has a healthy body weight for their height. Specifically, the value obtained from the calculation of BMI is used to categorize whether a person is underweight, normal weight, overweight, or obese.
These ranges of BMI vary based on factors such as region and age. Being overweight or underweight can have significant health effects, so while BMI is an imperfect measure of healthy body weight, it is a useful indicator of whether any additional testing or action is required.
BMI table for adults
This is the World Health Organization's (WHO) recommended body weight based on BMI values for adults. It is used for both men and women, age 20 or older.
| Classification | BMI range - kg/m² |
|---|---|
| Severe Thinness | < 16 |
| Moderate Thinness | 16 - 17 |
| Mild Thinness | 17 - 18.5 |
| Normal | 18.5 - 25 |
| Overweight | 25 - 30 |
| Obese Class I | 30 - 35 |
| Obese Class II | 35 - 40 |
| Obese Class III | > 40 |
BMI table for children and teens, age 2-20
The Centers for Disease Control and Prevention (CDC) recommends BMI categorization for children and teens between age 2 and 20.
| Category | Percentile Range |
|---|---|
| Underweight | < 5% |
| Healthy weight | 5% - 85% |
| At risk of overweight | 85% - 95% |
| Overweight | > 95% |
Risks associated with being overweight
Being overweight increases the risk of a number of serious diseases and health conditions. Below is a list of said risks, according to the Centers for Disease Control and Prevention (CDC):
- High blood pressure
- Higher levels of LDL cholesterol and triglycerides
- Type II diabetes
- Coronary heart disease and Stroke
- Gallbladder disease
- Osteoarthritis, a type of joint disease
- Sleep apnea and breathing problems
- Certain cancers
- Mental illnesses such as clinical depression, anxiety
- Generally, an increased risk of mortality
Limitations of BMI
Although BMI is a widely used and useful indicator of healthy body weight, it does have its limitations. BMI is only an estimate that cannot take body composition into account.
BMI cannot be fully accurate because it is a measure of excess body weight, rather than excess body fat. Older adults tend to have more body fat than younger adults with the same BMI. Muscular individuals and highly trained athletes may have higher BMIs due to large muscle mass.
The Ponderal Index (PI) is similar to BMI, but the main difference is the cubing rather than squaring of the height. The PI is more reliable for use with very tall or short individuals.